Contact assessment of balloon catheters

ABSTRACT

A medical apparatus and system for determining contact assessment includes a catheter having an elongate body having a proximal end, a distal end opposite the proximal end, and defining an injection lumen and an exhaust lumen, an expandable membrane defining a cooling chamber disposed at a point along the elongate body, the cooling chamber in fluid communication with the injection lumen and the exhaust lumen, and a contact assessment element which may be a temperature sensor located proximate the coolant return lumen for measuring an internal temperature of the chamber. The system may include the catheter, a console having a fluid supply, an exhaust path and at least one control mechanism operationally coupled to the temperature sensor for processing a temperature signal received from the temperature sensor. The apparatus and system can also have multiple electrodes to measure and process various impedances to determine contact assessment.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of patent application Ser. No.12/245,176, filed Oct. 3, 2008, entitled CONTACT ASSESSMENT OF BALLOONCATHETERS, now issued as U.S. Pat. No. 8,771,264, issued Jul. 8, 2014,and a continuation of patent application Ser. No. 11/129,205, filed May13, 2005 entitled CONTACT ASSESSMENT OF BALLOON CATHETERS, now issued asU.S. Pat. No. 7,442,190, issued Oct. 28, 2008, the entirety of which isincorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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FIELD OF THE INVENTION

The present invention relates medical systems, and in particular tomethods and systems for determining contact assessment.

BACKGROUND OF THE INVENTION

The experimental use of fluids with low operating temperatures, orcryogens, continues in the medical and surgical field. Of particularinterest are the potential use of catheter based devices, which employthe flow of cryogenic working fluids therein, to selectively freeze, or“cold-treat”, targeted tissues within the body. Catheter based devicesare desirable for various medical and surgical applications in that theyare relatively non-invasive and allow for precise treatment of localizeddiscrete tissues that are otherwise inaccessible. Catheters may beeasily inserted and navigated through the blood vessels and arteries,allowing non-invasive access to areas of the body with relatively littletrauma.

Catheter-based ablation systems are known in the art. A cryogenic deviceuses the energy transfer derived from thermodynamic changes occurring inthe flow of a cryogen therethrough to create a net transfer of heat flowfrom the target tissue to the device, typically achieved by cooling aportion of the device to very low temperature through conductive andconvective heat transfer between the cryogen and target tissue. Thequality and magnitude of heat transfer is regulated by the deviceconfiguration and control of the cryogen flow regime within the device.

A cryogenic device uses the energy transfer derived from thermodynamicchanges occurring in the flow of a refrigerant through the device. Thisenergy transfer is then utilized to create a net transfer of heat flowfrom the target tissue to the device, typically achieved by cooling aportion of the device to very low temperature through conductive andconvective heat transfer between the refrigerant and target tissue. Thequality and magnitude of heat transfer is regulated by deviceconfiguration and control of the refrigerant flow regime within thedevice.

Structurally, cooling can be achieved through injection of high-pressurerefrigerant through an orifice. Upon injection from the orifice, therefrigerant undergoes two primary thermodynamic changes: (i) expandingto low pressure and temperature through positive Joule-Thomsonthrottling, and (ii) undergoing a phase change from liquid to vapor,thereby absorbing heat of vaporization. The resultant flow of lowtemperature refrigerant through the device acts to absorb heat from thetarget tissue and thereby cool the tissue to the desired temperature.

Once refrigerant is injected through an orifice, it may be expandedinside of a closed expansion chamber, which is positioned proximal tothe target tissue. Devices with an expandable membrane, such as aballoon, are employed as expansion chambers. In such a device,refrigerant is supplied through a catheter tube into an expandableballoon coupled to such catheter, wherein the refrigerant acts to both:(i) expand the balloon near the target tissue for the purpose ofpositioning the balloon, and (ii) cool the target tissue proximal to theballoon's thermally-transmissive region to cold-treat adjacent tissue.

During the operation of a medical device in a therapeutic procedure,such as in a blood vessel, the heart or other body organ, the medicaluser desires to establish a stable and uniform contact between thethermally-transmissive region of the cryogenic device and the tissue tobe treated (e.g., ablated). In those instances where the contact betweenthe thermally-transmissive region of the cryogenic device and the tissueto be treated is non-uniform or instable, the resulting ablation orlesion may be less than optimal. It is desirable for the medicalprofessional to assess the state of the contact between thethermally-transmissive region of the cryogenic device and the tissue tobe treated, so that appropriate adjustments can be made to re-positionthe cryogenic device to obtain a more optimal contact and thus a moreeffective treatment.

It would be desirable to provide an apparatus and method of assessingthe quality of the contact between the thermally-transmissive region ofthe cryogenic device and the tissue to be treated, as well as monitoringand detecting any occurrences of fluid egress.

SUMMARY OF THE INVENTION

The present invention advantageously provides a method and system fortissue contact assessment.

One method for determining contact assessment includes the steps ofpositioning a catheter at a tissue treatment site, where the catheterhas a proximal end portion and a distal end portion, the proximal endportion defining at least one fluid inlet port and at least one fluidoutlet port, an expandable membrane defining a cooling chamber a coolantinjection lumen in fluid communication with the at least one fluid inletport and the cooling chamber, a coolant return lumen in fluidcommunication with the at least one fluid outlet port and the coolingchamber, the coolant injection tube, the cooling chamber, and theprimary coolant return lumen defining a fluid pathway and a temperaturesensor located near the coolant return lumen; measuring an internaltemperature of the chamber, and modifying the position of the catheterin response to the measured temperature.

A catheter having an elongate body defining an injection lumen and anexhaust lumen, an expandable membrane defining a cooling chamberdisposed at a point along the elongate body, the cooling chamber influid communication with the injection lumen and the exhaust lumen, afirst electrode located on the distal side of the expandable member, anda second electrode located on the proximal side of the expandablemember.

A medical system for determining contact assessment, the medical systemincluding a catheter having a proximal end portion and a distal endportion, the proximal end portion defining at least one fluid inlet portand at least one fluid outlet port, an expandable membrane defining acooling chamber, a coolant injection lumen in fluid communication withat least one fluid inlet port and the cooling chamber, a coolant returnlumen in fluid communication with at least one fluid outlet port and thecooling chamber in which the coolant injection tube, the coolingchamber, and the primary coolant return lumen define a fluid pathway,and a contact assessment element, such as a temperature sensor, locatedproximate the coolant return lumen. The medical system may furtherinclude a console having a fluid supply, an exhaust path, and at leastone control mechanism operationally coupled to the temperature sensor.The control mechanism may be a signal generator, a signal processor,impedance measurement system or any other control device. The contactassessment element may alternatively be a first assessment electrodelocated distal to the expandable member, and a second assessmentelectrode located proximal to the expandable member.

Another method for determining contact assessment includes the steps ofpositioning a catheter at a tissue treatment site, where the catheterhaving an elongate body defining an injection lumen and an exhaustlumen, an expandable membrane defining a cooling chamber disposed at apoint along the elongate body, the cooling chamber in fluidcommunication with the injection lumen and the exhaust lumen, a firstelectrode located on the distal side of the expandable member, and asecond electrode located on the proximal side of the expandable member,injecting an electrical current between the first and second electrodes,measuring an impedance between the first and second electrodes; and,modifying the position of the catheter in response to the measuredimpedance.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 illustrates a balloon catheter system in accordance with a firstembodiment of one aspect of the present invention; and,

FIG. 2 illustrates an embodiment of a shaft of the balloon cathetersystem of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an exemplary system 30 for performing cryogenicablation. The system 30 includes an elongate, highly flexible ablationcatheter 34 that is suitable for passage through the vasculature. Theablation catheter 34 includes a catheter body 36 having a distal end 37with a thermally conductive element 38 at or proximal to the distal end37. The distal end 37 and the thermally conductive element 38 are shownmagnified and are described in greater detail below. The catheter body36 has a proximal end 40 that is mated to a handle 42 that can includean element such as a lever 44 or knob for manipulating the catheter body36 and the thermally conductive element 38. In the exemplary embodiment,a pull wire 46 with a proximal end and a distal end has its distal endanchored to the catheter at or near the distal end 37. The proximal endof the pull wire 46 is anchored to an element such as a cam 48 incommunication with and responsive to the lever 44. The handle 42 canfurther include circuitry 50 for identification and/or use incontrolling of the ablation catheter 34 or another component of thesystem 30.

Continuing to refer to FIG. 1, the handle 42 can also include connectorsthat are matable directly to a cryogenic fluid supply/exhaust andcontrol unit or indirectly by way of one or more umbilicals. In thesystem illustrated, the handle 42 is provided with a first connector 54that is matable with a co-axial fluid umbilical (not shown) and a secondconnector 56 that is matable with an electrical umbilical (not shown)that can further include an accessory box (not shown). In the exemplarysystem the fluid supply and exhaust, as well as various controlmechanisms for the system are housed in a single console 52. In additionto providing an exhaust function for the ablation catheter fluid supply,the console 52 can also recover and/or re-circulate the cooling fluid.The handle 42 is provided with a fitting 58 for receiving a guide wire(not shown) that is passed into a guide wire lumen 60. During ballooninflation, contrast solution can be injected through the catheter'sinner guide wire lumen and into the pulmonary vein.

Still referring to FIG. 1, the thermally conductive element 38 is shownas a double balloon having a first membrane (e.g., inner balloon) 62contained or enclosed within a second membrane (e.g., outer balloon) 64,thereby defining an interface or junction 57 between the first andsecond membranes. The second membrane 64 provides a safeguard to preventfluid from leaking out of the cooling chamber 55 and into surroundingtissue should the first membrane 62, and therefore the cooling chamber55, rupture or develop a leak. The junction 57 between the first andsecond membranes 62, 64 may be substantially under a vacuum, such thatthe first and second membranes 62, 64 are generally in contact with eachother, with little or no open space between them. A coolant supply tube66 in fluid communication with the coolant supply in the console 52 isprovided to release coolant from one or more openings in the tube withinthe inner balloon 62 in response to console commands and other controlinput. A vacuum pump in the console 52 creates a low-pressureenvironment in one or more lumens within the catheter body 36 so thatcoolant is drawn into the lumen(s), away from the inner balloon 62, andtowards the proximal end of the catheter body. The vacuum pump is alsoin fluid communication with the interface or junction 57 of the innerand the outer balloons 62, 64 so that any fluid that leaks from theinner balloon 62 is contained and aspirated. Still referring to FIG. 1,the handle 42 includes one or more pressure sensors 68 to monitor thefluid pressure within one or both of the balloons, the blood detectiondevices 70 and the pressure relief valves 72. When coolant is releasedinto the inner balloon 62, the inner and the outer balloon 64 expand toa predetermined shape to present an ablation surface, wherein thetemperature of the ablation surface is determined by the materialproperties of the specific coolant selected for use, such as nitrousoxide, along with the pressure within the inner balloon 62 and thecoolant flow rate.

FIG. 2 illustrates an embodiment of a shaft or catheter body 36 of theballoon catheter system 34 of FIG. 1. The catheter body 36 includes amounting section 59 in communication with the proximal end of thermallyconductive element 38. The inner balloon 62 and outer balloon 64 arebonded to the mounting section 59. In this embodiment, the inner balloon62 and outer balloon 64 are bonded at different locations, which aredefined as the inner balloon bond joint 63 and the outer bond joint 65.In addition, several sensors are identified including a temperaturesensor 61 (e.g., thermocouple wire), leak detectors 67, 69 (e.g., leakdetection wires) and electrodes 90 and 92. In this embodiment, thetemperature sensor 61, is positioned at the proximal end of the balloonto measure the coolant flow after the liquid-to-gas expansion. Byplacing the thermocouple 61 at the proximal end of the balloon near thecoolant exhaust, the temperature for the balloon is measured. In thosesituations where the balloon maintains a stable and uniform contact withthe targeted tissue, the temperature of the balloon will remain in thecolder region, for example −75 to −90 degrees Celsius. If the balloon isnot in a stable and in uniform contact with the targeted tissue, thetemperature will be in a warmer region, for example −60 to −75 degreesCelsius. The difference in temperature indicates that there is anincoming blood flow around the balloon (i.e., the balloon is not inuniform contact with the treatment tissue) that causes the balloontemperature to increase because the blood flow acts as a convective heatsink. The control unit 52 can monitor the balloon temperature andprovide notification to the operator to terminate the current ablationprocedure and reposition the balloon for a more uniform and stablecontact with the treatment tissue. There has been an almost highcorrelation of fluoroscopy-visualized occlusion, inner balloontemperature, and electrical isolation of the pulmonary vein from theleft atrium.

In another embodiment, the contact assessment is provided by using thetwo electrodes 90 and 92 located on each side of thethermally-transmissive region 38 (e.g., a single balloon) and injectingan electrical current between the electrodes while measuring theimpedance between the electrodes 90 and 92 with an impedance measurementsystem 106. Electrical impedance measurement is obtained by passing acurrent of well-selected amplitude and frequency between two electrodesand measuring the differential voltage as produced across the sameelectrodes. After injecting a high frequency electrical current to thetwo electrodes 90, 92, the impedance can be measured by the impedancemeasurement system 106. The impedance measurement signal is thenprocessed using a signal processor (not shown) that can extract relevantdata from a specific frequency range to correlate the impedance changeto occlusion of the pulmonary vein. The electrical impedance of thetissue is much higher than the impedance of the blood, so measuring theimpedance between the first electrode 90 and the second electrode 92would indicate the efficacy of a balloon tissue contact. With highmeasurement sensitivity the system should be able to quantify thecontact quality. The impedance measurement system 106 providesinformation about the baseline impedance that may change as the balloon38 occludes a vessel, such as a pulmonary vessel (PV). As the balloonwill occlude or stop the blood flow between the proximal side and thedistal side of the balloon, the impedance at a defined frequency willincrease, which provides an indication of the quality of the contactbetween the balloon 38 and the treatment tissue.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A medical system for assessing contact with anarea of tissue, the medical system comprising: a catheter including: anelongate body having a proximal end, a distal end opposite the proximalend, and defining an injection lumen and an exhaust lumen; an expandablemembrane defining a cooling chamber disposed at a point along theelongate body, the cooling chamber in fluid communication with theinjection lumen and the exhaust lumen; a first electrode located distalto the expandable membrane; and a second electrode located proximal tothe expandable membrane; and a console including at least one controlmechanism operationally coupled to the first and second electrodes, theat least one control mechanism including a signal generator forproviding an electrical current between the first and second electrodesand a signal processor programmed to calculate an impedance measurementbetween the first and second electrodes.
 2. The system of claim 1,wherein the console further includes a fluid supply and an exhaust path,the fluid supply and the exhaust path each being in fluid communicationwith the cooling chamber.
 3. The system of claim 2, further comprisingan impedance measurement system.
 4. The system of claim 1, wherein thesignal processor is programmed to determine contact between theexpandable membrane and the area of tissue based on the impedancemeasurement between the first and second electrodes.
 5. The system ofclaim 4, wherein the catheter further comprises a handle portion coupledto the proximal end of the elongate body.
 6. The system of claim 5,wherein the handle portion includes catheter identification circuitry.7. The system of claim 5, wherein the handle portion includes at leastone pressure sensor in fluid communication with the cooling chamber. 8.The system of claim 5, wherein the handle portion includes a bloodsensor.
 9. The system of claim 5, wherein the handle portion includes apressure relief valve.
 10. The system of claim 4, wherein the signalprocessor is programmed to determine whether the expandable membrane isoccluding an anatomical vessel based on the impedance measurement. 11.The system of claim 1, wherein the electrical current is ahigh-frequency electrical current.
 12. The system of claim 1, whereinthe expandable membrane is a first expandable membrane, the catheterfurther including a second expandable membrane disposed about the firstexpandable membrane.
 13. The system of claim 12, wherein the firstexpandable membrane and the second expandable membrane define a junctiontherebetween.
 14. The system of claim 13, wherein the console furtherincludes a vacuum, the vacuum being in communication with the junctionbetween the first and second expandable membranes.
 15. A medical systemfor assessing contact with an area of tissue, the medical systemcomprising: a catheter including: an elongate body having a proximalend, a distal end opposite the proximal end, and defining an injectionlumen and an exhaust lumen; an expandable membrane defining a coolingchamber disposed at a point along the elongate body, the cooling chamberin fluid communication with the injection lumen and the exhaust lumen; afirst electrode located distal to the expandable membrane; and a secondelectrode located proximal to the expandable membrane; and a consoleincluding at least one control mechanism operationally coupled to thefirst and second electrodes, the at least one control mechanismincluding a signal generator for providing an electrical current betweenthe first and second electrodes and a signal processor programmed tocalculate an impedance measurement between the first and secondelectrodes, the signal processor being further programmed to determinecontact between the expandable membrane and the area of tissue based onthe impedance measurement between the first and second electrodes. 16.The system of claim 15, wherein the console further includes a fluidsupply and an exhaust path, the fluid supply and the exhaust path eachbeing in fluid communication with the cooling chamber.
 17. The system ofclaim 16, wherein the signal processor is programmed to determinewhether the expandable membrane is occluding an anatomical vessel basedon the impedance measurement.
 18. The system of claim 16, wherein theexpandable membrane is a first expandable membrane, the catheter furtherincluding a second expandable membrane disposed about the firstexpandable membrane.
 19. The system of claim 16, wherein the catheterfurther comprises a handle portion coupled to the proximal end of theelongate body, the handle portion including at least one of catheteridentification circuitry, a blood sensor, a pressure relief valve, andat least one pressure sensor in fluid communication with the coolingchamber.
 20. A medical system for assessing contact with an area oftissue, the medical system comprising: a catheter including: an elongatebody having a proximal end, a distal end opposite the proximal end, anddefining an injection lumen and an exhaust lumen; an expandable membranedefining a cooling chamber disposed at a point along the elongate body,the cooling chamber in fluid communication with the injection lumen andthe exhaust lumen; a first electrode located distal to the expandablemembrane; and a second electrode located proximal to the expandablemembrane; and a console including: a fluid supply; an exhaust path, thefluid supply and the exhaust path each being in fluid communication withthe cooling chamber; and at least one control mechanism operationallycoupled to the first and second electrodes, the at least one controlmechanism including a signal generator for providing an electricalcurrent between the first and second electrodes and a signal processorprogrammed to calculate an impedance measurement between the first andsecond electrodes, the signal processor being further programmed todetermine contact between the expandable membrane and the area of tissuebased on the impedance measurement between the first and secondelectrodes.